Magnetic displacement sensor arrangements with a primary coil and two secondary coils, with which a soft magnetic coupling element is associated, which is locally influenced by the magnetic field of a position encoder magnet for displacement measurement such that the relative position between the position encoder magnet and the coupling element can be determined, are described in the documents EP 0 693 673 A2, EP 0 238 922 A1 and DE 2 325 752, which are incorporated by reference.
Moreover, differential transformer displacement sensors are known. These are available e.g. in the form of LVDTs, “Linear Variable Differential Transformers”, wherein a soft magnetic core of the primary and secondary side coils is displaced and the displacement deflection of said soft magnetic core is recorded.
For digital displacement measurement it is known to digitize the electrical alternating voltage on the first and the second secondary coils and to digitally analyze it depending on the frequency of the excitation current or the excitation voltage through/on the primary coil(s) and thereby to determine the position or deflection or the displacement to be recorded.